Re: proc_file_read bug?

[Andreas Schwab <schwab@suse.de>]

Thomas Hood <jdthood@mail.com> writes:

|> I don't understand this part of proc_file_read() in 
|> fs/proc/generic.c:
|> 
|>                 /* This is a hack to allow mangling of file pos independent
|>                  * of actual bytes read.  Simply place the data at page,
|>                  * return the bytes, and set `start' to the desired offset
|>                  * as an unsigned int. - Paul.Russell@rustcorp.com.au
|>                  */
|>                 n -= copy_to_user(buf, start < page ? page : start, n);
|>                 if (n == 0) {
|>                         if (retval == 0)
|>                                 retval = -EFAULT;
|>                         break;
|>                 }
|> 
|>                 *ppos += start < page ? (long)start : n; /* Move down the file */
|>                 nbytes -= n;
|>                 buf += n;
|>                 retval += n;
|> 
|> When start >= page, we copy n bytes beginning at start and
|> increase *ppos by n.  Makes sense.  But what happens when
|> start < page?  We will copy n bytes starting at page, then
|> increase *ppos by start!!  What sense does that make?  If
|> there's cleverness happening here, someone please document it.

It is documented, RTFC.

Andreas.

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Andreas Schwab, SuSE Labs, schwab@suse.de
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